1. Field of the Invention
This invention relates, in general, to apparatus for providing hard copy outputs, such as copiers, duplicators, and printers and, more specifically, to such apparatus which stacks the output sheets into groups or sets and then binds or fastens the sheets together at their centers.
2. Description of the Prior Art
Several types of machines and devices are used to provide hard copy outputs, usually consisting of sheets of paper or transparencies. Although called copiers, duplicators, printers, and similar names, their function of providing one or more hard copy outputs of a desired page or sheet is basically the same. Once provided, the sheets can be ejected individually or in groups or sets of sheets arranged or bound together. Some types of apparatus perform additional finishing operations upon the sheets, such as folding and trimming.
A desirable final product for particular applications is a bound sheet set which is fastened at the middle of the sheets and folded into booklet form. Machines in the prior art providing such a booklet required trimming of the booklet edges after the folding operation in order to exactly align the edges of the booklet. This is necessitated by the fact that the outer sheets in the folded booklet extend around a larger bending radius and, consequently, the edges of these outer sheets become, upon folding, closer to the fold in the booklet than the more interior sheets.
Another problem associated with folded booklets provided by hard copy apparatus involves the placement of the images upon the sheets. Usually there are two images applied to the sheets before folding, with the images being positioned on each side of the fold line in the sheet and in proper sequence for correct page registration in the completed booklet. When the images for different sheets are positioned the same distance from the edge of the sheets, the image-to-edge distance, or border, changes when the booklet sheets are trimmed at the edges. This is because of the fact that the trimming cuts different amounts from the edges of the sheets, depending upon their distance from the center of the booklet. For example, the outermost sheet would be cut less than the innermost sheet, thus making the image on the outermost sheet farther from the outside edge than the image on the innermost sheet.
Therefore, it is desirable, and it is an object of this invention, to provide hard copy output apparatus which can provide fastened sheet sets suitable for folding without the need to trim the edges to achieve edge alignment. It is also desirable, and it is another object of this invention, to provide hard copy apparatus which can provide fastened sheet sets suitable for folding wherein the image borders will be consistent throughout the various pages of the folded sheet set.